Various proposals have been made to prevent jackknifing of articulated vehicles. For example, U.S. Pat. No. 4,241,934, dated Dec. 30, 1980, discloses a coupling device in which a pin mounted on a plate hinged to the front of the trailer is lowered into an arcuate slot in a structure fixed to the tractor frame. The slot limits movement of the pin and hence the extent to which the trailer can pivot relative to the tractor. The plate is lowered and raised by means of an hydraulic ram attached to the front wall of the trailer. U.S. Pat. No. 3,733,090, dated May 15, 1973, discloses a pair of pins mounted on the fifth wheel cooperating with spring-loaded bumpers mounted on the trailer to limit the maximum angular relationship of the tractor and trailer. U.S. Pat. No. 4,204,700, dated May 27, 1980, discloses a pair of pneumatic cylinders mounted on the trailer and cooperating with the fifth wheel assembly mounted on the tractor. Mounting pneumatic cylinders or dampers on the trailer, as taught by these prior proposals, is an expensive way to equip an entire fleet since there are perhaps four times as many trailers as tractors.
An anti-jackknifing coupling device which confines the modifications primarily to the tractor is disclosed in U.S. Pat. No. 3,850,449, dated Nov. 26, 1974, which discloses a fluid piston-and-cylinder link fastened at one end to the tractor, at a point spaced well forward of the fifth wheel assembly, and at the other end to the upper plate of the fifth wheel, so that pivoting of the tractor and trailer from the aligned position causes contraction of the fluid piston-and-cylinder link. This still requires a piston extending a significant distance from the fifth wheel assembly to a point near the cab of the tractor, which would not facilitate movement of the fifth wheel assembly longitudinally of the tractor to optimize the load distribution between the front and rear wheels of the tractor. Also, the piston-and-cylinder device would encroach upon useful space behind the cab of the tractor.
An object of the present invention is to provide an anti-jackknifing coupling device which is relatively economical to install on a fleet of articulated vehicles.
Another object of the invention is to provide an anti-jackknifing coupling device which controls rotational movement of the articulated units while permitting movement of the coupling position to and fro along the tractor.